Rolling method using prestressing

ABSTRACT

Process in which the prestress effort does not exceed, in value, that of the residual effort necessary for adjustments during rolling, it being necessary only to block the prestress circuit of the device after the product has been inserted.

I United States Patent 1 3,673,843 Dlolot July 4, 1972 I 1 ROLLING METHOD USING 3,464,245 9/1969 Dowsing et a]. ..72/24e PRESTRESSING 3,537,285 1|/1970 Kiggell et al, i i 4.72/3 ..72 237 Nwmy' {51333 $32??? 724237 IT ADSKIBHLL Smiete Nouvelle Spidem, Pll'h, I runee FORHMN PNWNTS 0R APPLICNHONS ml I,l6l,7l5 8/]969 Great Britain .12/245 [21] Appl. N0.: 871,905 4,317,9l6 7/1969 Japan ..72/245 P E M'lt S. M h {30] Foreign Application Priority Data Z2 e r Oct, 28, 1968 France ..68l7l662 [57] ABSTRACT U-S. Pro e in which the preslregs effort does no! EXCCCd in value. [5]] f "Rubin/32 that of the residual effort necessary for adjustments during Fleld 0f sflll'ch 246 rolling, it being necessary only to block the prestress circuit of the device after the product has been inserted. [56} References Cited 3 Claims, 5 Drawing Figures UNITED STATES PATENTS 3,398,559 8/1963 Tracy 72/245 PATENTmJuLJ I972 3573.843 sum 10? 3 FIG! I l l PATENTEU L 4 I 2 sumanf 3 FIG.3

PATENTEBJUL 4 1912 SHEET 3 Bf 3 FIG. 4c!

LEFT FRAME x I l a I HIS. 4b

ROLLING METHOD USING PRES'IRESSING Many types of rolling mills have already been proposed which use prestressing. In this connection the applicant has already discussed his own ideas on the subject, more particularly in his French Pat. No. l,3l4,562 of Dec. 1, 196l, to which there have been two additions, the first under No. 90470 of May 24, 1966, and the second under N0. PV 147,83l ofApr. ll, 1968.

The present invention has as its object to provide an improved rolling method using prestressing.

ln order to bring out the features of the invention, to begin with a theoretical discussion of the question in general will be held; new notations will also be introduced by the applicant in order to facilitate and clarify the following discussion.

Thus, it has been thought necessary to bring in the idea of elastic chains in a rolling mill.

By elastic chain" there is understood the mean line followed by the resultant of the forces produced during rolling or which may have been created previously to this operation, in the cross-sections of the various components of a rolling mill. Applied to a rolling mill of the type using prestressing, here assumed to be of the four-high type, this concept leads to a differentiation between three separate elastic chains, all three starting at two specific points which are symmetrical relatively to one another with respect to the median horizontal plane of the rolling mill and coinciding with the lines, on the section plane, of the contacting edges of the journals of the two backing-up rolls, upper and lower, with the corresponding bores of the respective chocks.

For the sake of convenience in the following explanation, these two points will be called A and B.

The three chains in question are as follows:

a first chain, referred to as the long chain," which extends over the entire height of each stand housing, extends through the clamping device of the rolling mill and affects the various wedging means, and also the upper and lower parts, respectively, of the upper and lower backing-up chock bodies, to tenninate at the aforesaid points A and a second chain, referred to as the roll chain," again starting from the same points A and 8, passes successively through the four rolls of the rolling mill and also through the product being rolled, when the latter is engaged; third chain, referred to as the short chain" or prestressing chain, starting from the aforesaid points A and B, passes successively through the lateral portions of the backing-up roll chock bodies and the jacks for regulating the spacing between the said chock; in the particular case of the rolling mill according to the invention, which derives from that described by applicant in his French Pat. No. 1,489,069 of Apr. 22, 1966, the said third chain also passes through the auxiliary blocks fixed to the interior of each stand, right against the housings of the said stand, the said blocks being intended to serve as supports for the aforesaid spacing regulating jacks, these jacks being also made to act as prestressing jacks in the particular case of embodiment being dealt with.

FIG. 1 shows very diagrammatically a sectional view of a rolling mill stand in which the three chains, which have just been discussed, have been outlined.

In the following description, F F, and F, will be used to refer to the respective forces produced in each of the aforesaid chains.

Then three coefficients will be defined, k,, k, and k referred to as yielding coefficients, each representing the deformability of the chain with which it is associated, that is to say, the quotient of the deformation undergone by the said chain, this deformation being related to the force F produced in the chain. By their dimensions, these coetficients are the inverse of the rigidities of the corresponding chains.

However, it is important to stress that it is not possible to consider the results obtained by calculation and expressed by means of the coefficients k as being the inverse of the expressions which would have been obtained by starting from the usual elasticity coefficients.

To illustrate more fully the behavior during rolling of the three elastic chains of the machine, this behavior could be compared to that of a system of springs occupying substantially the respective positions of the various chains. FIG. 2 shows an illustration of this kind.

The long chain is likened to a tension spring tensioned between the points A and B, the action of which tends to make these two points approach one another.

The prestressing chain III is compared to a compression spring situated between these same points A and B which it tends to move away from one another, the opposite effect to the preceding spring.

Finally, the roll chain [1 is compared to a set of two leaf spring elements bearing on the points A and B for elastically opposing any increase in the size of the gap J between the rolls.

If this invention is applied to a stand of a conventional rolling mill without prestressing, which is the equivalent of dispensing with the corresponding compression spring in the equivalent diagram, it is found that the total yielding coefficient of the stand is obtained by adding to one another the deformations which correspond to those undergone by the two springs during the course of rolling.

In other words,

If this same representation is then applied to a rolling mill stand with prestressing of the type recommended by the present invention and referred to as a mill stand with blocked prestressing," that is to say, a rolling mill having the essential characteristic of having its prestressing circuit blocked only after engagement of the product and not before, as is normally done, it is found that everything happens as if, the chains l and Ill being in parallel with one another, the total yielding coeffi cient of the stand is obtained by adding to that of the second chain a compound coefficient corresponding to the chains I and Ill together, put in parallel.

Such compounding of yielding coefficients follows from the fact that, by their nature, these various coefficients can be treated as electrical resistances (the forces developed along each of the chains being then likened to intensities) and, more particularly, can be added to one another in the case of series connections, whereas in the case of parallel connections it is their reciprocals which are added to one another.

Therefore, for the rolling mill stand according to the invention the formula would be:

In order to see more clearly the meaning of the variations in the total yielding coefficient of the stand, it will be assumed.

kg 8 "k It follows that:

It will then be seen that when n becomes very great, I: tends towards a critical value, k k,, which means that the in fluence of k, disappears completely (this case would be that of the sort chain with a very high yielding coefficient, which substantially comes back to the situation with a conventional rolling mill without prestressing); conversely, when this same yielding coefficient is very slight, tending even toward 0 (in the case of a short chain which is extremely rigid), the yielding coefficient of the stand is reduced to only the coefficient k,, that is, to the yielding of the rolls.

This discussion provides an opportunity for showing the advantage obtained by using a rolling mill with prestressing according to the invention, that is to say, with blocked prestressing. In fact, comparing the yielding coefficient of a conventional rolling mill, without prestressing, to that of a rolling mill according to the invention and assuming, for reasons of convenience, that the coefficients of the three chains of the latter are equal (k, k It k), the yielding of a convention stand is given by:

K 2k, whereas that of a stand with blocked prestressing is:

K=k +k/2=3k/2 Therefore, the useful effect, that is to say, the reduction in yielding, is 25 percent. This reduction is also greater in pro portion as k; is smaller; thus for:

k 2 m the reduction obtained is 33 percent,

The foregoing shows very clearly one of the features of the method according to the invention: the possibility of keeping the coefficient k, to the smallest possible value compatible with the result intended.

The elastic chain concept permits, in addition to the deduc tions discussed hereinbefore, noting the way in which the vari ous forces produced in it mill behave during the cycle of operations to which the mill is subjected.

Using a system with three closed chains, in equilibrium with one another, the vectorial equation F, 1 if, is always satisfied.

Considering, on the other hand, the absolute values of the forces in question, we have:

since this equation expresses the fact that the forces produced in the chain 1 counterbalance the total of those produced in chains II and Ill.

It is useful to know the incidence on F, and F of the possi ble variations of the force F or AF We have:

AF =AF,AF (l) The variations of F 3 are therefore of opposite sign to those of F the variations of F l are of the same sign.

In each chain, the yielding, that is to say, the increase in the distance AB, is expressed by the product of the corresponding yielding coefficient and the variation of the force produced in the chain, Thus,

in the first chain, there is a yielding of k, AF,

in the third chain, a yielding ofk AF these two yieldings being, of course, equal, we have:

By means of the results thus established it is possible to analyze as follows the various adjustments to be made in a rolling mill in accordance with the rolling method according to the invention.

First of all, however, the case of prestressing before engagement of the product will be examined with, as a complementary hypothesis, the existence of an interroll gap J (J 0).

The second chain not being initially loaded, the variation AF, of the corresponding force will be numerically equal to the rolling force, which value has to be taken into account in formula (3).

The variation AF, being negative, it will be seen that the prestressing F continually decreases, the said decrease being proportional to the rolling force.

A study of the variations of AF, as a function of those of k shows that the greater the rigidity of the short chain, the greater will be the proportion of the rolling force absorbed by this third chain. In the limiting case, that is to say, for a chain k, which is infinitely rigid, it could absorb the whole of the rolling force.

In accordance with the method according to the invention, the foregoing conclusion gives the upper limit of the prestressing force to be imparted initially to the system (taking into account, however, a corrective factor which will be dealt with hereinafter). One of the advantages obtained by the invention should be noted here, in taking into account the existence of the upper limit in question: it is useless dimensioning the machine for higher prestressing values, and also it will be sufficient to provide this machine with a hydraulic central station, the capacity of which will not have to exceed that of the critical prestressing force which has just been defined.

As for the corrective factor to be additionally introduced, this is a marginal force, referred to as a residual force, which should be available on the short chain in order to permit effecting any possible clamping corrections, as will be discussed hereinafter.

Having examined the case of prestressing produced before engagement of the product, assuming the existence of an in terroll gap, consideration will now be given to the case where the work rolls are "rolling," that is to say, in contact with one another, before the product is engaged. The variation F, of the force in the roll chain can then assume any positive values, from a very small minimum value corresponding to the smallest thickness of the product to be rolled, up to the maximum value which is, by definition, the rolling force.

Even more clearly than in the preceding case, it will be shown hereinafter that according to the invention it is useless to take the prestressing beyond a certain value which is notably less than the values usually employed before the invention.

A rolling force of 1,000 metric tons will be used, and it will be assumed that the three chains of the stand have the same yielding coefficient (k, k, k,,).

In the present case formula (3) will be as follows if the interroll gap J is positive:

1P =1 K,/(k,+ k F l I residual forcel Assuming that the residual force is fixed in advance at l00 metric tons, there will be, before engagement, in the short chain:

F llxl ,OOO-HOO 600 metric tons. But, as soon as the product is engaged, the prestressing will absorb, by definition, the fraction:

k,/(k, k:,) F rolling, or

1% l,000 metric tons 500 metric tons.

Therefore, after engagement there will remain a prestressing of:

F; 600 metric tom 500 metric tons metric tons only,

and it is known that the force in the long circuit will be:

P, F, F 1,000 l00= 1,100 metric tons. Similar reasoning shows that, if engagement were effected with a rolling contact force of L000 metric tons, that is to say, if there were:

AF 2 F rolling initial rolling contact F =0, the total prestressing, normally intended to compensate for the fraction ll( 1 s) of the variation in force AF}, would have been:

a I/( l k AF, F residual but, in the long run, this prestressing would be reduced to F; F residual, which proves that it is unnecessary to regulate the prestress higher than 100 metric tons, the value fixed for the residual force.

The incidence of corrections made from the clamping force during the execution of a pass on the product being rolled should be examined separately.

To make such correction possible, it is necessary to effect the deliberate opening of the long chain: The corresponding variation AF, will be balanced by the variations of the two other forces in accordance with the formula (1) from which there is derived:

AF, AF, AF, The deformation of the gap AB will be considered, in both Chain II and Chain III, which gives:

it, AP, k, AF, in magnitude and in direction.

Putting together formulas (l and (4), the following is obtained:

z a/( 2+ a) r which is true only if the deformations of the product during the course of treatment under the effect of the variation of the rolling force are disregarded.

It will be seen in this case that it is appropriate to limit the rigidity of the short chain to a reasonable value, otherwise the F clamping correction introduced into the long chain would be absorbed by the said short chain for the greater part and to no advantage. By way of example, if it is assumed that the short chain is three times more rigid than the roll chain, that is to say, 0

k l/n) k and n36, it would follow that:

AF ViAF,

and consequently,

It will therefore be seen that if it is desired to obtain a correction AF, of IO metric tons on the product, the corresponding value of the increase in clamping force AF, will have to be 40 metric tons of which 30 will pass, without any useful effect, in the form ofa AF force increase, into the short chain.

Reasoning to the contrary, it is found that with the method according to the invention it is necessary, when effecting an unclamping correction, to always keep the short chain under tension, the minimum value of the correction being obtained by:

F (k k;,)/l: X residual force.

It now becomes possible to state clearly the two essential rules of the prestressing rolling method according to the invention.

The first rule prescribes that, for the initial setting of the prestressing before engagement, it is useless to exceed the value which has been given in the case in question for the residual force in the short chain.

The second rule states that after having adjusted the prestressing in accordance with the first rule it is ad vantageously possible, from the instant when the product to be rolled is engaged, to isolate the prestressing circuit from the source of fluid under pressure which supplies it.

Before finishing with the considerations of a general order on the method as described by the invention, it should be stressed that the general formulas (I (2), and (3) are symmetrical relatively to the coefficients k, and it which are, consequently, transposable, but without the value of K being modified.

This leads to a very remarkable result for rolling mills using the said method: it is possible, optionally, to choose as the prestressing chain either the long chain or the short chain; it is sufficient to interpose, by suitable connection of the hydraulic circuits in question, plunger jacks in the elastic chain which will not be subjected to prestressing.

This remark assumes its full value when the transformation of an existing rolling mill is begun in order to bring it into accordance with the invention. One or the other of Chains I or III will then be chosen for applying prestressing thereto, depending on the facilities which will be found on the site, in both of these hypotheses.

Other features and advantages of the invention will be brought out from the course of the following description and with reference to the accompanying drawings, description and drawings concerning the preferred form of embodiment of the invention, which is given purely by way of illustration and is not intended to be limiting in any way.

In the following drawings, the same reference numerals are always used to designate the same parts.

The two first figures attached to the present description have already been discussed hereinbefore:

FIG. I which shows diagrammatically a longitudinal section through a four-high rolling mill according to the invention, this section being taken on a vertical plane parallel to the direction of rolling, solely for the purpose of showing the various elastic chains being discussed.

FIG. 2 which is a diagrammatic representation of the elastic chains of the rolling mill according to FIG. I, these chains being compared to springs.

In addition:

FIG. 3 shows, again diagrammatically, the rolling mill of FIG. 1 to which there have been added on the one hand the two plunger jacks as described by the applicant in his French Pat. No. 1,215,820 of Oct. I9, 1958, and on the other hand the various parts constituting the hydraulic control system of the apparatus, the said parts being suitably interconnected.

FIGS. 40 and 4b are diagrams showing, respectively, a first and a second possibility of interconnecting the components shown in FIG. 3 and depicting both sides of the rolling mill.

FIG. 1 shows one of the sides of the rolling mill stand comprising the two uprights l, the upper and lower cross-members 2 and 3 respectively, the work rolls 4 and backing-up rolls 5, the work roll chocks 6 and backing-up roll chocks 7, the blocks 8 fitted internally on each of the uprights, the jacks 9 between the chocks, the product 10 being rolled, and the lower jack II.

The figure shows the points A and B defined hereinbefore which are the points of intersection, with the plane of the figure, of the contacting lines between the journals of the back-up rolls and 101 designates the long chain comprising, at each side, the upright I, the lower jack 11, the various wedging means (not shown) and the upper and lower parts of the upper and lower backing-up roll chock elements 7.

I02 designates the roll" chain comprising, again between the points A and B, the two pairs of rolls 4 and 5, the said chain also passing through the product being rolled if any such product is engaged between the rolls.

I03 designates the prestressing short chain assumed here to comprise the chain which comprises, again from the points A and B, the lateral parts of the backing-up roll chock element 7, the regulating and prestressing jacks 9 and the auxiliary blocks 8.

The comparison of the three elastic chains of the rolling mill according to FIG. 1 to a system of springs is shown in FIG. 2 in the following way:

The points A and B have been assumed to be subjected to the simultaneous action of a certain number of springs. A first tension spring 201 is fixed between these points which, under its action, tend to approach one another. A second spring, a compression spring this time, is fixed between the same points A and B which it tends, contrary to the first spring, to move away from one another. Finally, a third system, composed of two leaf spring elements 202 which are substantially parallel, is also assumed to be fixed in such a manner that the ends situated at the same side of each of these leaf elements are respectively fixed to the points A and B, the gap 1 between the leaf elements representing the interroll gap of the mill; in the initial setting, referred to as the rolling contact" setting, the gap J is reduced to nil, the two leaf elements 202 being in contact at their two centers, with or without an initial compression force.

The increase in the distance AB during rolling represents the yielding of the rolling mill, and it will be seen immediately that, owing to the force developed here, in its long chain, the rolling mill resists the yielding and that conversely the two leaf spring elements, subjected to the rolling force at their centers, act in the sense of lengthening the distance AB, the intensity of this action being moderated by the fact that the said two points might tend to move away from one another, this tendency being precisely facilitated by the action of the prestressing spring 203.

FIG. 3 shows the rolling mill of FIG. 1, adding thereto the control and driving elements indispensible for making it operate in accordance with the precepts of the method according to the present invention.

First of all, 12 designates the two plunger-piston jacks, these jacks being of the type having a small cross-section and a long travel. These two jacks are interconnected mechanically as indicated by the French Pat. No. l,2l3,820, already mentioned belonging to the present applicant.

Then the figure also illustrates what might appropriately be called the "hydraulic central control system" of the rolling mill, that is to say, the assembly constituted by the operating fluid pumps, their driving motors, the pressure regulator and the control elements such as electromagnetic valves and nonreturn valves.

in order to show more clearly the interchangeability of the two Chains l and Ill, the hydraulic connections between the rolling mill and the parts connected therewith have not been fully drawn; the inlets and outlets of the various parts have simply been indicated by means of capital letters, the corn binations which can be obtained by permutating the circuits in question being defined hereinafter by means of bigrams or trigrams composed of the said letters combined with one another in accordance with the line of the connections which have to be achieved.

The various references in the figure have the following meanings.

The jacks 12 have rods such as 13 driven each in rotational movement, directly or inversely, by a bevel reduction gear 15, the driving axes of the two reduction gear units being arranged in prolongation of one another and made dependent on motors 14.

The pumps [6 and 25 are driven by the motors l7 and 26 and comprise also at least one common strainer 18 immersed in the tank 19, 20 is a pressure regulator, 21 and 22 being electromagnetic valves terminating in non-return valves 23 and 24.

As for the various inlets and outlets, they are defined as follows:

Assuming that the frame represented on the figure is the right-hand frame, relatively to the rolling direction, X and Y are the inlets of the jacks 9 between checks of FIG. 1. (U) and (V) designate the corresponding inlets of the jacks having the same function which are contained in the left-hand frame of the rolling mill, this being not shown.

In a similar way, Z designates the inlet of the lower jack of the righthand frame, (W) designating the inlet of the lefthand jack having the same function.

R and S are the respective outlets of the jacks 12 at the right and left. Finally, M and N are the two outlets of the hydraulic central control system of the machine.

it will be seen then that it is simply necessary to make the connections:

R to Z (S) to M to X andto(U) NtoY and to(V) in order to make the rolling mill operate as discussed hereinhefore, namely, so that the prestressing" circuit is that which comprises the interchock jacks 9, the clamping circuit being then the circuit of the lower jacks ll each connected to the plunger jack corresponding thereto, an invariable fluid volume being imprisoned between the jacks thus interconnected at each side of the machine. This type of connection is illustrated in FIG 4a where it can be seen that the hydraulic source is connected to the secondary clamping system, while the hydromechanical regulating circuit is connected to the primary clamping system.

When on the contrary it is the combination:

R to X to Y (S) to(V) andto(U) MN to Z and to (W) which has been brought about, the situation is again that in which the two chains have been transposed, the long chain then serving as the prestressing chain and the short chain as then serving as an inverse clamping chain. The outlets M and N can then be merged in a single outlet from a single valve. This type of connection is illustrated in FIG. 4b where it can be seen that the hydraulic source is connected to the primary clamping system, while the hydromechanical regulating circuit is connected to the secondary clamping system.

The apparatus described in the first of the two foregoing hypotheses operates as follows:

When the prestressing circuit is not subjected to pressure, the rolling mill behaves like a traditional rolling mill, here a mill with hydromechanical clamping; the rigidity of the short chain being nil, the total yielding coefficient is given by k 0 When, on the contrary, prestressing is to be provided, the pressure in the short chain is first of all regulated to a value fixed in advance, as explained hereinbefore, and then the product is engaged and the electromagnetic valves 22 and 21 are closed in that order, which blocks the corresponding circuit; the total yielding coefiicient of the rolling mill becomes:

in the case of the second hypothesis the symmetrical conclusions will be easy to draw, transposing k, and k throughout.

it will be seen also in FIG. 3 that the apparatus according to the invention makes it possible to obtain, in addition to the regulations already described, the immediate compensation of an accidental deviation which may happen in the travel of the product owing to a dissymmetry which appeared in the hard ness of the product or as a consequence of a lack of parallelism of a temporary nature occurring between the generatrices at which the work rolls exert their pressure on the product during rolling.

The results achieved have a very high standard of precision; they even seem to be capable of exceeding the orders of mag nitude of the precision which is possible with the most improved measuring apparatus for measuring product thicknesses. Therefore, these latter apparatus set the present limits along this line of development.

It goes without saying that the foregoing description has been given only by way of a non-[imitative example, and that many modifications may be made without thereby departing from the framework of the invention or going beyond its scope.

That which is claimed is:

l. In a method of operation of a four-high rolling mill having (a) slidable chocks, (b) back-up rollers supported by said chocks, (0) work rollers in engagement with said back-up rollers, (d) a primary clamping system for urging the work rollers of the rolling mill towards one another through said chocks and said back-up rollers, (e) a secondary clamping system for urging said chocks away from one another, (f) a hydraulic source associated with one of said clamping systems, (g) a hydromechanical regulating circuit associated with the other of said clamping systems. the improvement comprising the following steps:

A. starting the operation of the rolling mill,

B. actuating the clamping system associated with said hydraulic source to establish a first pressure for prestressing the rolling mill, said hydraulic source supplying a continuous pressure of a magnitude ensuring a prestressing force at most equalling the residual force necessary for correction during the rolling operation,

C. actuating the clamping system associated with said hydromechanical regulating circuit to establish a second pressure,

D. introducing the work into the bight of the work rollers subsequent to the aforedefined steps and E. blocking the clamping system associated with said hydraulic source subsequent to step (D) to simultaneously isolate said hydraulic source from the last-named clamping system and to captivate the hydraulic fluid in the latter.

2. [n a method as defined in claim 1, including the step of connecting said hydraulic source to said primary clamping system and connecting said hydromechanical regulating circuit to said secondary clamping system.

3. In a method as defined in claim 1, including the step of connecting said hydraulic source to said secondary clamping system and connecting said hydromechanical regulating circuit to said primary clamping system.

i i I! i ll! W UNITED S'I'A'I'ES PA'IHN'I ()FFHIE C ERTI FICATE O F CO R RECTION Patent No. 3, 673, 843 Dated July 4, 1972 Inventor(s) Lucien Diolot It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 4, line 75, "F3 F residual" should read F F residual Col. 8, line 9, "R to X to Y" should read R to X and to Y Signed and sealed this 2nd day of January 1973.

(SEAL) Attest:

EDWARD M.FLETC IHER,JR. ROBERT GOTTSCHALK Attestlng Offlcer Commissioner of Patents 

1. In a method of operation of a four-high rolling mill having (a) slidable chocks, (b) back-up rollers supported by said chocks, (c) work rollers in engagement with said back-up rollers, (d) a primary clamping system for urging the work rollers of the rolling mill towards one another through said chocks and said back-up rollers, (e) a secondary clamping system for urging said chocks away from one another, (f) a hydraulic source associated with one of said clamping systems, (g) a hydromechanical regulating circuit associated with the other of said clamping systems, the improvement comprising the following steps: A. starting the operation of the rolling mill, B. actuating the clamping system associated with said hydraulic source to establish a first pressure for prestressing the rolling mill, said hydraulic source supplying a continuous pressure of a magnitude ensuring a prestressing force at most equalling the residual force necessary for correction during the rolling operation, C. actuating the clamping system associated with said hydromechanical regulating circuit to establish a second pressure, D. introducing the work into the bight of the work rollers subsequent to the aforedefined steps and E. blocking the clamping system associated with said hydraulic source subsequent to step (D) to simultaneously isolate said hydraulic source from the last-named clamping system and to captivate the hydraulic fluid in the latter.
 2. In a method as defined in claim 1, including the step of connecting said hydraulic source to said primary clamping system and connecting said hydromechanical regulating circuit to said secondary clamping system.
 3. In a method as defined in claim 1, including the step of connecting said hydraulic source to said secondary clamping system and connecting said hydromechanical regulating circuit to said primary clamping system. 